Peterson 1935. Zapus July 23. 6 mi. SW Mountain City, Cobb Creek, 6500 ft., Elko Co., Nevada. Two caught close to creek, one at water's edge, other on bank few feet from water - first ones ever caught by any member of any of Dr. Hall's Nevada expeditions, according to Dr. Hall. July 24. 6 mi. SW Mountain City, Cobb Creek, 6500 ft., Elko Co., Nevada. Nine caught along Cobb Creek, in grassy area near creek + on dry slope covered with grass + sage brush. July 25. 6 mi. SW Mountain City, Cobb Creek, 6500 ft., Elko Co., Nevada. Nine caught in identical places as per July 24. One male Zapus had large amount of subcutaneous fat, necessitating much scraping in preparation of skin; other had no excess fat. Bone present in penis. In addition to usual essential organs of reproduction, male has a bicornuous structure composed of a thin membrane apparently filled with fluid resembling the two horns of the uterus of a female in appearance + position, only anterior ends of the horns are blind + are not hung by a mesentery. One other species of mouse, which is now beyond recall, possessed similar structure developed to lesser degree: either Peromyscus m. sonorensis or Perognathus p. aliscoensis(?)